A movable storage rack with shelf units mounted, thereon which can be moved by means of a driving force imparted to its driven wheels by manual rotation of a rotatable handwheel located on the exterior section of the movable storage rack, is conventionally known. When a number of these movable storage racks are arrayed on rails laid on the floor, any desired storage rack may be moved, creating a working aisleway between that rack and the adjacent one, so that access is made possible to the materials stored in those two racks only, while the other movable storage racks stand in compact form, allowing efficient utilization of a room in which space is limited. However, these movable storage racks may move of their own accord at times, because, for example, of the slope of the floor, or because the rails on which the wheels ride are for some reason inclined. In addition, regardless of the fact that a certain aisleway has already been opened and someone is working in the area, there is the danger of another person, unaware of this, attempting to open an aisleway between two other storage racks, causing the first person to be jammed between the two racks where he is working. Accordingly, the installation of locking devices has been proposed with the objective of preventing such inadvertent movement of a storage rack. One example of such a locking device is described in Japanese Utility Model Publication No. 38420/1980.
However, such prior art locking devices on movable storage racks have been installed in a location removed from the rotatable handwheel used to impart motion to the movable storage rack, and a series of operations involving unlocking, rotating the rotatable handwheel, and relocking repeatedly, means that the operator must release his hold on the rotatable handwheel to manipulate the lock, and vice versa, and the operation becomes very inconvenient.